How much soil fills a raised bed?
Multiply inside length by inside width by actual fill depth. Multiply again by the number of matching beds. Use internal dimensions rather than the outside frame dimensions. Convert depth from inches to feet before multiplying. The calculator reports cubic feet, cubic yards and liters so that you can compare supplier units without confusing volume with bag weight.
Worked example: one 4 × 8 bed
A bed measuring 8 feet by 4 feet filled 12 inches deep needs 32 cubic feet before any allowance. That is approximately 1.19 cubic yards or 906 liters. With two-cubic-foot bags, the purchase count is 16 bags. At an illustrative eight currency units per bag, the bagged subtotal is 128. A bulk quote uses the unrounded cubic-yard quantity, subject to the supplier’s ordering increments.
Choose the fill depth deliberately
The frame height is not always the depth you need to fill. Existing soil, a partially filled bed or deliberate headspace can change the remaining volume. Enter only the depth of material being purchased. If the base has an irregular shape, measure several locations and prepare separate estimates where necessary. This rectangular model cannot determine a hidden slope or the volume occupied by buried objects.
Compare bags and bulk
Read the volume on the bag label. Weight alone cannot tell you how much space soil will fill, because moisture and material composition vary. Bag quantities round up to whole bags; bulk volume is shown without a supplier-specific order increment. The two cost outputs therefore answer slightly different purchasing questions. Add delivery charges and minimum order requirements before deciding which option is cheaper.
Extra allowance and settling
The allowance input increases the estimated purchase volume. Zero means the measured geometric space only. No universal settling percentage is built into the tool. Ask the supplier how its product behaves and whether the quoted volume is loose or settled. Repeated watering or material decomposition can change the bed level over time. An allowance is a scenario, not a guarantee of final soil depth.
Several beds and soil mixtures
The bed-count field repeats the same dimensions. For beds with different sizes, calculate each group and combine the unrounded volumes before deciding on bags. A soil blend is a separate choice from the total volume. The calculator does not prescribe a universal mixture or assess nutrient levels. Use gardening guidance suitable for your plants, drainage and local conditions when choosing the material.
Questions and method
Does this tell me how many kilograms to buy? No, kilograms measure mass and require a suitable bulk density. Can I use centimeters? Convert them to the clearly labeled feet and inches before entry; liter results are provided for purchasing. Does the bulk estimate include delivery? No. The arithmetic is volume divided by bag volume, with whole-bag rounding and your optional purchase allowance.
Method and review: these examples follow the equations described above. Mississippi State Extension: raised-bed volume. Use the applicable supplier specification or institutional regulation for the assumptions. Written by Velour Trends · Updated 8 November 2026. Report a calculation issue.